Crystalline semiconducting polymers can be chemically doped with molecular dopants via integer charge transfer to highly conductive states, where charge carriers in high-mobility, semicrystalline polymers undergo band-like transport. Although coherent, band-like transport characteristics are indispensable for further improvement of conductivity, the correlation between band-like transport and crystallinity in doped conjugated polymers has not been comprehensively studied. Here, we investigate the role of crystallinity in molecular-doped thiophene-based semiconducting regioisomers. The doping efficiency and band-like transport were examined using X-ray diffraction and magnetotransport measurements, which revealed clear differences between regioisomers due to the differences of their polymer packing structures and crystallinity.